Got an email from Dave, who's currently shooting a short film in the delightfully named "Dumbo" area of Brooklyn. ("Where you headed?" "Dumbo." "Pipsqueak.") Says The Dave:

I was shooting my own short film down in Dumbo (part of Brooklyn), [Edit: I just said that!] and I passed by a sign and another crew setting up. It was the set of Synecdoche! They have a great location. It's being shot in this part of Brooklyn that consists mainly of warehouses with the Manhattan skyline in the background across the water. Parts of the roads are still cobblestone from way back when. I might lurk by the set over the next few days. They have been shooting a bunch of scenes in the warehouse section of Dumbo.

I'll bet those are going to be the warehouse scenes.

So now we know, if Synecdoche doesn't float our boat, we can watch the movie that's going on in the distant background instead.